At least 38 civilians have been killed and 65 wounded in a suicide attack at a shrine in northwestern Baghdad, Iraqi government officials said.

An interior ministry official put the death toll at 40, including 17 Iranian pilgrims.

The blast occurred on Sunday at a checkpoint outside of the Imam Moussa shrine in Kadhimiya, where a female bomber targeted Shia pilgrims.

"A woman wearing an explosive belt blew herself up near one of the gates of the shrine," Major General Qassim Atta, an Iraqi spokesman for security operations in Baghdad, said.

"According to our first preliminary report, 35 were killed and 65 injured. Most of them were Iranian pilgrims and women and children," Atta said, describing the force of the blast as "very big".

The pilgrims were participating in a ritual procession related to Ashura, which falls on January 7 and is the end of the 10-day mourning period that marks the killing of Imam Hussein, the grandson of Prophet Muhammad.

Despite the chaos caused by the blast, people continued to converge on the shrine, the most important religious site in Baghdad for Shia Muslims.